Differential deposition and utilization of backfat layers in swine.

Growing pigs were nutritionally manipulated to study depletion, depletion followed by repletion or deposition of the individual backfat layers. Obese and lean pigs were used to gain insight into the possible role of genetic selection for backfat depth on each backfat layer. Backfat depth, including individual layers was measured in live pigs at sequential times by ultrasonic methods. At a variety of anatomical locations, change in backfat expressed as a rate or as percentage change during both depletion and deposition was greater in layer 2 than layer 1 (outermost). Genetically obese pigs increased backfat depth by accretion of layer 2 to a greater extent than layer 1. Genetically lean pigs had more equal accretion of the two layers with a preference toward layer 1 in some cases. Selection for total backfat depth appears to have selected layer 2 in preference to layer 1. Backfat layer 1 changed to a small extent compared to layer 2 during depletion, deposition or genetic selection possibly indicating a greater metabolic role in vivo for layer 2.